1. Technical Field
This invention relates to polymers containing reactive functional groups and to products obtained therefrom. This invention also relates to a method for appending cyclic polyanhydride groups to vinyl halide polymers by reacting a mixture of hydroxyl functionalized polyvinyl halide and a cyclic polyanhydride functionalizing agent. These functional copolymers are useful in the formation of a wide variety of polymer systems having a variety of physical and chemical properties that may be tailored to specific end uses.
2. State of the Art
Polyvinyl halide resins particularly polyvinyl chloride (PVC) resins have enjoyed a great deal of success as a material which may be formed into a wide variety of useful articles. The ease at which PVC can be molded, extruded, calendered or formed as well as its low cost, has contributed to this success.
PVC by itself is a tough and hard polymer. To enable it to be processed into useful articles, it has been proposed to add to the PVC processing aids, such as plasticizers and lubricants, or to form blends with other monomeric and/or polymeric compounding ingredients. Processing aids are normally incorporated into PVC during what is normally called a compounding operation. The PVC is worked on mill rolls and the processing aid(s) is added and milled into the polymer. This mixing can also be performed with internal mixers or other mixing equipment all of which is known in the art. PVC compositions made with processing aids perform very well in most applications. However, these compositions have a tendency to migrate out of the PVC over extended periods of time. This migration phenomenon can lead to problems in some products. For instance, PVC will become more brittle as the plasticizer migrates out, thus leading to cracking and loss of flexibility of the PVC article. In certain medical and food applications such as, for example, blood bags, medical tubing, food wrap and beverage containers, migrating processing aids may be extracted by the contents of the container leading to contamination.
In another approach to the processing problem, it has been proposed to prepare blends of polymers which maximizes the processing and/or physical properties of the component polymers. However, these attempts have generally been unsuccessful. Blends of different types of polymers are often incompatible, resulting in a marked deterioration or loss of physical properties characteristic of each of the unblended polymers. The polymers tend to become cheesy during processing, making it extremely difficult to disperse any desired additives uniformly throughout the blend. Even where the two polymer components are compatible during melt processing, they often tend to separate into segregated domains of individual polymer components.
Because of these drawbacks, various attempts have been undertaken to prepare polymer compositions that are easily processable and which possess improved physical properties. In this regard, many methods have focused upon the preparation and use of functionalized polymers having pendant reactive groups which facilitate the grafting of materials and other polymers to form graft-modified polymers and polymer blends having improved physical properties. The preparation of graft-modified resins by grafting carboxyl-functionalities to a substrate polymer via the reaction of an anhydride and a polymer reactive therewith is known. It is also known that the carboxyl-functionalized polymers thusly obtained may subsequently be further modified with compounds containing free hydroxyl groups. However, the prior art is directed to methods of forming carboxyl-containing polymers and products obtained thereby and not to polymers containing pendant cyclic anhydride groups.
U.S. Pat. No. 4,382,128 discloses a method for preparing carboxyl-modified polyolefins comprising the steps of: (1) reacting a thermally degraded polyolefin with an unsaturated polycarboxylic acid, ester or anhydride which is graft polymerizable therewith; and (2) reacting the carboxyl-functionalized polymer thusly obtained with a polyhydroxy compound to obtain compositions having improved heat distortion, strength and flexual modulus. The reaction of the polyhydroxy compound with the carboxyl-functionalized polymer is preferably conducted in the presence of solvents.
U.S. Pat. No. 4,506,056 discloses a method for preparing carboxyl-containing polymers comprising mixing together maleic anhydride, a free radical copolymerization initiator, an additive which inhibits the homopolymerization of maleic anhydride and a substrate polymer. The ingredients are mixed above the melting point of the substrate polymer in a suitable mixing device yielding a carboxyl-functionalized polymer. Suitable substrate polymers include vinyl halide, e.g., vinyl chloride.
In U.S. Pat. No. 4,680,361 there is disclosed a crosslinked polymer coating composition comprising carboxyl-functionalized lactone acrylates. These compositions are derived from a reactive monomer unit prepared from the reaction of hydroxyalkyl acrylate and epsilon-caprolactone, said monomer unit is subsequently reacted with an anhydride to produce a monomer containing carboxyl groups. The monomer so prepared can be homopolymerized or copolymerized with other ethylenically unsaturated monomers, including vinyl halide.
Basically, however, all of the foregoing methods have disadvantages. Reacting a carboxyl-functionalized substrate polymer with a polyhydroxy compound in the presence of a solvent as disclosed in U.S. Pat. No. 4,382,128 is disadvantageous from the standpoint that solvents are generally difficult to handle, pose environmental hazards and are difficult to dispose of. The melt processable carboxyl-functionalized polymers disclosed in U.S. Pat. No. 4,506,056 require the addition of free radical initiators and certain polymerization inhibitors during their preparation, leading to complex formulation problems. Moreover, the carboxyl-functionalized polymers thusly obtained would be difficult to derivatize with hydroxy containing materials due to the nature of the transesterification reaction. Transesterification is an equilibrium reaction. To shift the equilibrium in the direction favoring products, it would be necessary to utilize large excesses of the hydroxy containing compound or to remove products from the reaction medium. This would require extra process steps and added operation costs.
The disadvantage inherent in the method taught in U.S. Pat. No. 4,680,361 are the multitude of reaction products contained in the polymer composition. For example, this patent is directed to crosslinked compositions comprising polymerizing one or more ethylenically unsaturated monomers with a composition comprising:
(a) 0 to 10 weight percent, preferably 0 to 5 weight percent of a lactone;
(b) 0 to about 10 weight percent of hydroxyethyl acrylate or methacrylate;
(c) 0 to about 2 weight percent, preferably 1 or less weight percent, of one or more diacrylates;
(d) 0 to about 10 weight percent, preferably 5 or less weight percent, of products resulting from Michael addition, acrylate polymerization, transesterification reactions, or other side reactions;
(e) 0 to about 50 weight percent, preferably 0 to about 20 weight percent, of a reactive monomer of the following average formula: ##STR1##
wherein R.sup.5 is a divalent radical, R.sup.2 is either hydrogen or methyl, each of R.sup.3 and R.sup.4 is hydrogen, phenyl, or lower alkyl having 1 to about 6 carbon atoms, x is an integer having a value of up to about 10, and y is an integer having a value up to about 20;
(f) 0 to 20 weight percent, preferably less than 10 weight percent, of the reaction product of hydroxyethyl acrylate or methacrylate and an anhydride; and
(g) remainder to 100 weight percent of a reactive monomer of the following average formula: ##STR2## wherein R is H, methyl or ethyl, R' is an alkylene radical having 2 to about 12 carbons, R" is an alkylene radical having about 1 to about 10 carbons, R'" is a divalent radical having 2 to about 20 carbons, m is an integer having a value of 1 to about 20, preferably 1 to about 10, most preferably 1 to 5, and z is an integer having a value of 1 to about 4, preferably 1 to 2.
It is readily apparent from the foregoing that many competing side reactions may occur during the homo- or copolymerization of the above reactive monomer composition. For example, unwanted crosslinking may occur during the homo- or copolymerization of the reactive monomer composition in the presence of the diacrylates as disclosed under item (c) above.
Accordingly, it would be highly desirable to provide a method for preparing a polymer resin which is substantially pure and free from polymerization contaminants and which has improved physical properties by means of an improved process which can be run in a single reaction vessel. None of the foregoing disclosures teach or suggest such a method or polymer product obtained thereby.